Abstract Identifying the mechanisms that regulate CD8 T cell responses is critical for improving anti-viral and anti-tumor vaccine efficacy and is currently an area of intense investigation due to the profound implications for improving human health. The goal of this application is to determine the mechanism(s) by which Plac8 expression is reg- ulated in CD8 T cells, gain insights into Plac8's biochemical functions in CD8 T cells, and importantly, deter- mine how Plac8 enhances memory CD8 T cell formation.Memory CD8 T cells are superior in protecting indi- viduals from reinfection with highly mutagenic, evolving pathogens like influenza, HIV and malaria. This is pri- marily due to the fact that CD8 T cells, unlike antibodies, recognize conserved, internal proteins that are requi- site for pathogen survival. Moreover, memory CD8 T cells correlate with improved overall survival in many cancers, emphasizing the broad benefits of memory CD8 T cell vaccines to human health. However, CD8 T cell responses to some live attenuated vaccines are not maintained long-term which results in waning im- munoprotection. Therefore, methodologies to improve CD8 T cell based vaccines are warranted and depend- ent on a better understanding of the factors that regulate the development and maintenance of these long-lived memory cells. Our preliminary data demonstrate that the novel cysteine-rich protein, placenta-specific 8 (Plac8), is highly expressed in CD8 T cells, is induced by IL-12 and is critical for the development and/or maintenance of CD8 T cell memory due to its functions within the T cells, themselves. However, how Plac8 regulates CD8 T cell responses is unknown. In this application, we will bring together expertise in the fields of molecular and cellular T cell immunology to comprehensively dissect how Plac8 regulates CD8 T cell func- tions, including their early effector functions and the formation and maintenance of memory CD8 T cells. In Aim 1, we will examine the regulation of Plac8 in murine and human T cells and use standard immunological ap- proaches as well as an unbiased RNA-Seq approach to gain insight into its functions through the identification of novel Plac8-dependent pathways. In Aim 2 we will use a murine influenza infection model to test the hy- pothesis that Plac8 regulates autophagy, a process that can mitigate the cellular stress associated with effector to memory (ETM) cell transition. These data are essential to advance our understanding of Plac8 functions in T cells that underlie the generation of host protective CD8 T cell memory responses, a primary goal of vaccina- tion.